1. Field of the Invention
This invention concerns a radial-flow variable-capacity turbine which may be used as a supercharger (an exhaust turbocharger) for an internal combustion engine. This type of radial-flow variable-capacity turbine is so constructed that the operating gases pass through a number of variably angled nozzle vanes from a coil-shaped scroll in the turbine casing, and the gases are made to flow to the turbine rotor so that they drive the rotation of the rotor.
2. Description of the Related Art
In recent years, if an internal combustion engine has a supercharger, it has become more and more common for it to be the kind of supercharger with a variable-capacity turbine. Such a turbine varies the flow rate of the exhaust gases transported from a coil-shaped scroll to the turbine rotor according to the operating state of the engine, and it does this variation in such a way as to match the flow rate of the engine exhaust gases to that rate which would produce the optimal operating condition of the supercharger.
FIG. 5 shows an example of a supercharger with a variable-capacity turbine belonging to the prior art. FIGS. 6 and 7 show how a link plate 3, lever 1 and nozzle vane 2 are connected. FIG. 6 is a partial frontal cross section (taken at a right angle with respect to the shaft of the turbine). FIG. 7 is a cross section taken along line Bxe2x80x94B in FIG. 6.
In these drawings, 10 is a turbine casing and 11 is a coil-shaped scroll in the outer periphery of the turbine casing 10. Number 12 is a turbine rotor, which is supported on a center casing, in such a way that it is free to rotate, by bearings (not pictured). The rotor is coaxial with the compressor (also not pictured).
Number 2 is a nozzle vane, a number of which are arranged in spaces along the circumference of the turbine on the inner periphery of the scroll 11. Nozzle shafts 02, on the inner extremity of the nozzle, are supported in nozzle mounts 4, which are fixed to the turbine casing 10, in such a way that they are free to rotate so that the angle of the nozzle vane varies. Number 14 is a gas exhaust casing which guides the exhaust gases out of the engine once the gases have completed the work of expanding to drive the turbine rotor 12. The gas exhaust casing is fixed to the turbine casing 10.
Number 3 is a disk-shaped link plate. It is supported by the turbine casing 10 in such a way that it is free to rotate. Indentations 3a are provided along the periphery in which levers 1, which will be discussed shortly, can engage. Number 07 is an actuator which drives nozzle vanes 2 through the link plate 3. 005 is a lever which connects actuator rod 7 of the actuator 07 to the link plate 3.
FIGS. 6 and 7 show how the link plate 3, levers 1, and nozzle vanes are assembled. The indentations (oblong holes) 3a are provided on the inner periphery of the disk-shaped link plate 3 at regular intervals along the circumference of the turbine. Bosses 01, formed on the outer extremities of levers 1, engage in the indentations (oblong holes) 3a in such a way that they can rotate and scrape the surface of the indentation. The nozzle shaft 02 of each aforesaid nozzle vane 2 is fixed to the inner extremity of one of the levers 1.
In this sort of variable-capacity turbine, the reciprocating displacement of the actuator 07 is transmitted to the link plate 3 by way of actuator rod 7 and lever 005 of the crank mechanism, thus driving the rotation of the link plate 3. When the link plate 3 rotates, the bosses 01 of the levers 1 which are engaged in indentations 3a of the link plate 3 move along the circumference of the link plate. Nozzle shafts 02, which are fixed to the interior extremities of the levers 1, rotate. This causes nozzle vanes 2 to rotate, changing the vane angle.
In the variable-capacity turbine pictured in FIGS. 5 and 6, bosses 01 on the outer extremities of levers 1 engage in indentations 3a, which are provided on the inside of disk-shaped link plate 3 at regular intervals along the circumference of the turbine. The nozzle shafts 02 of nozzle vanes 2 are fixed to the interior extremities of the levers 1.
With this existing design, then, each link plate 3, lever 1 and nozzle vane 2 are all arranged in virtually the same plane in a radial direction toward the center, and at regular intervals along the circumference of the turbine. As a result, the outer diameter of the variable nozzle mechanism which consists of the link plate 3, lever 1 and nozzle vane 2 is quite large, with the result that it is difficult to fit the variable nozzle mechanism at the inner side of scroll 11 in turbine casing 10. Thus the variable nozzle mechanisms must be placed in the center casing in which the bearing for turbine rotor 12 is mounted. The more the variable nozzle mechanism protrudes from scroll 11 in the axial direction and ends up in the center casing, the longer the axial dimension of the variable-capacity turbine. This increases the size of the variable-capacity turbine and makes it more difficult to install in an automobile.
With this sort of existing design, the nozzle adjustment and drive mechanisms, which comprise a complicated series of links, are housed in the center casing where the bearing and seals are installed. This complicates the design of the center casing, resulting in more assembly and disassembly processes and making installation more difficult.
In view of the problems which occur with the prior art design, the objective of this invention is to provide a variable-capacity turbine in which the nozzle adjustment mechanism, comprising a link plate serving as the drive component and a lever and nozzle vane serving as the connector mechanism, would all be housed at the inner side of the scroll in the turbine casing. This would reduce the axial length of the turbine and make it more compact, and thus easier to install in a car. It would also avoid the problem of the center casing becoming too complex. There would be fewer assembly and disassembly processes, and the turbine would be easier to install.
To solve these problems, the invention of a first preferred embodiment comprises a variable-capacity turbine which has a coil-shaped scroll in the turbine casing, a number of nozzle vanes which are arranged along the circumference of the turbine at the inner peripheral side of the scroll, which are supported on the turbine casing in such a way that they can rotate, and which vary the vane angle, and a turbine rotor which rotates freely on the inner periphery of the nozzle vanes. The operating gases are made to flow from the scroll through the nozzle vanes to the turbine rotor, driving the rotation of the rotor. This variable-capacity turbine is distinguished by the following. The turbine has a nozzle adjustment mechanism having a nozzle drive member for the nozzles which is connected to an actuator that causes the nozzle drive member to rotate around the turbine shaft, and a plurality of connectors to link the nozzle drive member to the nozzle vanes. The nozzle adjustment mechanism, which comprises the nozzle drive member and the connectors, is installed in the link chamber provided inside the scroll, and the link chamber providing the nozzle adjustment mechanism is gas sealed against the operating gas chamber and is provided at the gas outlet side of the nozzle vanes.
The nozzle drive member may consist of a disk-shaped link plate, the link plate having a series of oblong holes along the circumference of the turbine shaft, and the oblong holes being provided at a specified angle with respect to a radial line which passes through the turbine shaft. The connectors are provided between the nozzle vanes and the disk-shaped link plate along the circumference of the turbine shaft. The connectors consist of levers, one end of which is fixed to one of the nozzle vanes, and the other end of which has a boss on it. This boss engages in the oblong holes in the nozzle drive mechanism in such a way that it can rotate and slide along the surface of the holes.
The invention second preferred embodiment is distinguished by the following. The nozzle drive member consists of a disk-shaped link plate, and the link plate has a series of oblong holes along the circumference of the turbine shaft, and the oblong holes are provided at a specified angle with respect to a radial line which passes through the turbine shaft. The connectors consist of levers which are provided at the gas outlet side of the disk-shaped link plate, one end of which is fixed to one of the nozzle vanes, and the other end of which has a boss on it. This boss engages in the oblong holes in the nozzle drive mechanism in such a way that it can rotate and slide along the surface of the holes.
With these embodiments, the lever and link plate, which form the nozzle adjustment mechanism, are arranged in a link chamber which is further inside the turbine than the scroll, and the mechanism is provided at the gas outlet side of the nozzle vanes. This arrangement allows the lever and link plate of nozzle adjustment mechanism to be placed further inside the turbine than the scroll without requiring that the exterior diameter of the scroll be increased. The axial length of the nozzle adjustment mechanism is contained almost entirely within the diameter of the scroll. Thus the axial dimension of the variable-capacity turbine is shorter than in prior art designs, allowing the supercharger to be made more compact.
Further, as has been discussed above, the nozzle adjustment mechanism is placed further inside the turbine than the scroll, so it need not, as in prior art designs, be made to fit into the center casing where the bearing and seal mechanism are installed. This avoids complicating the design of the center casing, reduces the number of assembly and disassembly processes needed, and makes the turbine easier to install.
Also, as we have discussed, bosses of arm-like levers engage in oblong holes of the link plate, which is set at a fixed angle with respect to a radial line passing through the turbine shaft. The reacting force on the actuator caused by the gas pressure, which depends on the nozzle vanes and the frictional force experienced by the various components of the nozzle adjustment mechanism, can be reduced without increasing the arm length of the lever. As has been discussed, the axial dimension of nozzle adjustment mechanism can easily be made to fit within the scroll. This allows the length of the axial dimension of the variable-capacity turbine to be reduced so that the supercharger can easily be made more compact.
In the second preferred embodiment of this invention, one end of lever has a boss which protrudes toward the link plate, that is, it protrudes inward (toward the link plate). The link mechanism which connects the link plate to actuator is arranged inside along the axial line of the turbine. This allows the total length of the turbine to be reduced so that the turbine can be made more compact.